1. FIELD OF THE INVENTION
This invention relates to heat exchangers used in flight vehicles to cool avionic equipment, and more particularly to a closed loop skin heat exchanger which maintains a constant, thermodynamically optimal gap between the fuselage skin and the onboard liner and, since rivets or mechanical fasteners are not employed, is easily installed and removed to provide ready access to the fuselage.
2. DESCRIPTION OF THE PRIOR ART
Presently, avionics systems are cooled by circulating the air heated by the systems through a radiator situated in a forward facing air scoop. The scoop breaches the otherwise smooth continuity of the skin of the aircraft, thus subjecting the aircraft to increased aerodynamic drag and negatively effecting the performance of the vehicle.
This solution is also prone to failure from the clogging of the scoop by foreign objects such as birds, or fracture of the radiator core by smaller objects. The probability of failure from clogging can be reduced by employing multiple scoop radiators, but this further increases aerodynamic drag. The probability of fracture of the radiator can be reduced by strengthening the material used in the core, but this entails increased expense and weight, the latter further penalizing the performance of the vehicle.
Conventional air conditioning also presents a means to cool the avionics equipment, but this apparatus is heavy, expensive, and requires constant maintenance. An air conditioning unit obtains the work necessary for its operation from a vehicle engine, and thus adversely effects the engine's performance and increases its fuel consumption.
Also used are cooling systems which simply direct cold ambient air over or through the equipment to be cooled. However, this solution exposes the equipment to the risk of contamination and damage from particulate matter and water.
Conventional skin heat exchangers create an envelope that includes the internal structural support members which abut and project above the fuselage skin by simply positioning a flat rigid liner high enough above the highest projecting support member to provide an air passage between the support member and the liner. this inevitably results in the distance between the liner and the skin being too high for efficient heat exchange; or, where the liner is positioned at minimal distance above the projecting support member, a constriction of the flow through the envelope which similary defeats efficient heat exchange.
Attempts to contour the liner to more closely follow the profile of the projecting support member as it rises above the level of the fuselage have used rigid metal fasteners to attach the contoured section of the liner to the projecting support member, as well as fasteners to attach the lower, level portion of the liner to the fuselage skin. Liners contoured and attached in this conventional fashion are heavy and also quite difficult and time consuming to remove and reinstall when maintenance or structural damage require access to the fuselage. Additionally, the means of attachment typically include rivets that pass through the fuselage and protrude above the otherwise smooth surface of the outer skin. This increases the aerodynamic drag of the aircraft and, additionally, creates stress risers, that is, locations in the skin where stress is increased, and, therefore, where the potential for structural failure is greatest. The fact that the liner is rigid and firmly attached to the structural support members and the skin also negatively effects skin and fuselage stress characteristics and performance parameters.
All conventional cooling apparatus are installed during the assembly of the flight vehicle because it is quite difficult and time consuming, if not impossible in some instances, to subsequently install them.